Automated Model Dredger

Yessir

Member
Thought I would just share the project which I have been working on for the last 18 months with you.
I originally built the model of the Mannin dredger about 8 years ago, with everything being operated via radio control. Unfortuantely sailing the model (controlling throttle & rudder) and controlling the dredger (operating the crane & grab) at the same time was quite a challenge and regularly resulted in crashing the model! I started looking at how I could automate the dredger part of the model so that it could look after itself whilst I concentrated on sailing.
Enter a Picaxe 18x and SD21 servo control board. The model works in two modes. In Manual mode the 18x counts pulses from the receiver and outputs it to control the crane as if radio controlled. In automatic mode the 18x runs through a pre set routine to perform dredging operations automatically.
The video clip show the model operating at a public exhibition (hence the background noise) dredging gravel from a barge and dropping it into the hopper. Hopefully follow this up with some video of it operating on the water in a few weeks time.

http://www.youtube.com/watch?v=IX4rpG9x8As
 

BeanieBots

Moderator
Nice model. Well done.

Do you exhibit at either of the large south UK shows?
ie, Hop Farm and/or Brighton Center.
If yes, I'll keep an eye out for you.
 

Yessir

Member
Unfortunately I don't attend any shows in the south of England, however I probably will be exhibiting at the Birchwood show near Warrington on August bank holiday weekend.

I have attached a couple of photographs showing the SD21 board and wiring before installation and then one when it is all fitted inside the boat. It is a bit cramped 'under the covers', so it is difficult to get a true picture of the Picaxe installation and how it is wired.
 

Attachments

BeanieBots

Moderator
It doesn't look like you are using very many channels on the SD21.
If you are pushed for space, maybe consider the AXE020 board.
It would require a little more effort doing servo sequences but it can control 8 servos and is quite a bit smaller.

Shame you can't make down south. Unlikely that I can make it up to Warrington
 

westaust55

Moderator
Well built model and a good clear video of the operation.

Any chance the you might post some PICAXE program code to share with others. Many here look to projects with RC control and/or servo motors.
 

Yessir

Member
Actually using 6 servo outputs at the moment (jib up / down, crane slew left / right, crane bucket up / down, bucket open / close, hopper doors open / closed, smoke on / off) there are also some digital outputs controlling LED's which light / flash depending on program status. Some of the servos have been modified to work as winches by removing feedback potentiometer and fitting limit switches to each end of the travel.

I would actually like a few more inputs so that I can read more outputs from the receiver so that more functions can be controlled manually. Waiting fot 18M2 (which should be a direct replacement) which should allow me to configure more pins as inputs. Future plans also include an LCD display to provide information about the model and also a countdown timer until the next display (at exhibitions the model runs for about 10 minutes and then waits about 10 minutes before the next display). Lots of people ask "how long until the next display"!

Yessir.
 

Yessir

Member
More Video

I have uploaded a bit more video of the dredger, this time on the bench with teh covers removed so that you can see the internal mechanism when working.

Each function is controlled by a radio control servo, some of which have been modified to remove the feedback potentiometer and provide a continuously rotating winch. You will notice a number of microswitches on the model which are wired to stop the servos when the winches get to each end of their travel. A diode soldered across the microswitch allows the servo motor to be reversed.

http://www.youtube.com/watch?v=r24NeVCt-EI
 
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hippy

Senior Member
I think there's always something about a working model which has a little extra sparkle and captures an audience. The stack smoke is a nice touch - though hopefully not a servo working over the limit :)

Very nice work.
 

Marcwolf

Senior Member
Beautifully done - a real work of art.

I have a couple of questions - with the winch servo - is it a multiturn servo or are you using a microswitch as a limiter. I did look at one of the tail winch servo's from HiTec and also got a couple of 4 turn servo's from another company that worked very well.
But due to size I ended up rolling my own so to speak out of 9gram servos..

I have modified my own SD21 to take a 28X2 module and that gives me a few extra inputs and outouts. One only needs to cut 4 traces and swap them about for the I2C functionality. The 18M2 is a good drop-in fro the 18X but I needed more variables and the scratchpad area that the 28X2 offered.

I also noticed that yours using the internal SD21 low voltage regulator - thats a very handy feature.

Your project is definately one I tip my hat to.
Take Care
Dave
 

Yessir

Member
Beautifully done - a real work of art.

I have a couple of questions - with the winch servo - is it a multiturn servo or are you using a microswitch as a limiter. I did look at one of the tail winch servo's from HiTec and also got a couple of 4 turn servo's from another company that worked very well.
But due to size I ended up rolling my own so to speak out of 9gram servos..

I have modified my own SD21 to take a 28X2 module and that gives me a few extra inputs and outouts. One only needs to cut 4 traces and swap them about for the I2C functionality. The 18M2 is a good drop-in fro the 18X but I needed more variables and the scratchpad area that the 28X2 offered.

I also noticed that yours using the internal SD21 low voltage regulator - thats a very handy feature.

Your project is definately one I tip my hat to.
Take Care
Dave
I initially experimented with multi turn servos by replacing the internal potentiometer with a multi turn one, but the problem with that solution is as the servo nears its end point it takes absolutely ages to slow down and stop with continuously reducing torque.

For the dredger operation there is a lot of 'start a servo moving', 'wait a number of seconds' and then 'stop the servo', so I decided to just disconnect the internal potentiometer from the output shaft and fit micro switches into the motor circuit. The micro switches are actually a 'failsafe' when using manual mode - the picaxe looks after the timings in automatic mode. I am also using the speed reduction function in the SD21 to accelerate & decelerate one of the servos at the end of its travel.
 
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